the battery is fully charged and the reading from the alternator is the same as the battery about 11.8the battery is fully charged and the reading from the alternator is the same as the battery about 11.8

hey i appreciate the response my dad is a mechanic..lol however he thinks it could be a computer what do you think? il also check the others.hey i appreciate the response my dad is a mechanic..lol however he thinks it could be a computer what do you think? il also check the others.

I'm just thinking that if your dad is a mechanic, then have him disassemble the alternator and see if he can see anything wrong. Assuming you've wired up the alternator correctly, I am just suspect that there are no brushes in the alternator, or the regulator is bad.

Are you measuring alternator output at the alternator, or at the battery? If at the battery, and you don't have it wired correctly, then you will not see anything but battery voltage. If you check voltage at the alternator output, and it's higher than battery voltage, then there is something wrong in the wiring, either incorrectly wired, or a bad connection somewhere, as the voltage goes to the power distribution block.Check that there is not a fuse for the alternator in the fuse panel. It may be the original alternator somehow caused a fuse to fail. It could be that there is no field power from the battery feeding the alternator through that circuit.

ECM is unlikely. One way to tell for sure, go to a repository library and see if they have the factory service manuals (not Haines or Motors or Chiltons) for your specific vehicle. They usually have complete troubleshooting charts, wiring diagrams, everything you need that the dealers use.

ECM is unlikely. One way to tell for sure, go to a repository library and see if they have the factory service manuals (not Haines or Motors or Chiltons) for your specific vehicle. They usually have complete troubleshooting charts, wiring diagrams, everything you need that the dealers use.

You might have them check and se that you are getting the right alternator.it could also be because of the battery not pushing enough volts back to the alternator that is keeping the reading off. have the battery tested and see if you have a dead cell or low reading on it

is the voltage regulator inside the alternator on that vehicle? i cant remember right off if it is or not. does the belt have enough tension on it?is the voltage regulator inside the alternator on that vehicle? i cant remember right off if it is or not. does the belt have enough tension on it?

you may need a bigger battery too i didnt think about that..cold cranking amps should be around 750 or so..you may need a bigger battery too i didnt think about that..cold cranking amps should be around 750 or so..

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Afraid not. Although the light goes out it still may not be charging very little charge will put the light out. the other reason I feel it's the alternator is instead of rpm increasing it should decrease as a properly charging alternator should pull the engine which should decrease the rpm

Run this by me one more time your Post doesn't make sence. Is Battery light on? Is alternator working properly 13 to 14 Volts You Must have a fully charged Battery to test. Get tested at your Local Auto Parts Store after charging

The ECU has no control on the voltage. Does your vehicle have a separate voltage regulator? If so that's your fault. A lot of alternators have the regulator built into them. The alternator needs to be put on a test rig away from the vehicle and the output tested, this will eliminate the vehicle, You could disconnect the wiring to the alternator, run three fly leads to the alternator and to a separate battery and run the engine and test the voltage on the spare battery. Wire 1: Battery neg to case of alternator Wire 2: Battery pos to + terminal on alt (the thick wire) Wire 3: Battery pos through a 5 watt bulb to the ind terminal (ignition light) 17 volt will blow another battery for sure.

Your car's symptoms (voltage fluctuations under load that shouldn't happen) seem tostrongly indicate that your voltage regulator has failed. The voltage regulator is the componentthat regulates voltage coming from the alternator, and which is supplied to the rest of the car.Your new belt tensioner indicates to me (and should have to your mechanic) that thealternator and/or voltage regulator weren't able to operate properly, and a faulty belt tensionerhas killed more than one car's alternator/voltage regulator.Your do not need new headlights. Do fix the turn signals.

In the 2005 Sunfire, the voltage regulator is an integral component of the alternator, and isnot separately serviceable. So your 2005 Sunfire needs a new alternator.

The national parts chains (Advance Auto Parts, AutoZone, Pep Boys) will (for free) administera "Charging System Test." Which will telly you for sure that your alternator/voltage regulatoris bad. Do this before replacing alternator, since its a pricy part in the 05 Sunfire.

Just in case, Here's the 2005 Sunfire manual entry on (a) Diagnosis & testing the alternator, and(b) replacement of the alternator

Alternator replacement is a do-it-yourself project, though you may need to get a"Serpentine Belt Kit" on your favorite parts store's loan-a-tool program to remove/re-install the serpentine (drive) belt.======================================================================Diagnosis & Testing - 2005 Pontiac Sunfire Alternator

Alternator Load Test

1. With the engine running, turn on the blower motor and the high beams ( or other electrical accessories to place a load on the charging system).

2. Increase and hold engine speed to 2000 rpm.

3. Measure the voltage reading at the battery.

4. The voltage should increase at least 0.5 volts from the voltage test. If the voltage does not meet specifications, the charging system is malfunctioning. NOTE Usually under and overcharging is caused by a defective alternator, or its related parts (voltage regulator), and replacement will fix the problem; however, faulty wiring and other problems can cause the charging system to malfunction. Many automotive parts stores have alternator bench testers available for use by customers. An alternator bench test is the most definitive way to determine the condition of your alternator.

Alternator No-Load Test

1. Connect a tachometer to the engine. CAUTION Ensure that the transmission is in Park and the emergency brake is set. Blocking a wheel is optional and an added safety measure.

2. Turn off all electrical loads (radio, blower motor, wipers, etc.)

3. Start the engine and increase engine speed to approximately 1500 rpm.

4. Measure the voltage reading at the battery with the engine holding a steady 1500 rpm. Voltage should have raised at least 0.5 volts, but no more than 2.5 volts.

5. If the voltage does not go up more than 0.5 volts, the alternator is not charging. If the voltage goes up more than 2.5 volts, the alternator is overcharging. NOTE Usually under and overcharging is caused by a defective alternator, or its related parts (regulator), and replacement will fix the problem; however, faulty wiring and other problems can cause the charging system to malfunction. Many automotive parts stores have alternator bench testers available for use by customers. An alternator bench test is the most definitive way to determine the condition of your alternator.

6. If the voltage is within specifications, proceed to the next test.

Voltage Test

1. Make sure the engine is OFF , and turn the headlights on for 15-20 seconds to remove any surface charge from the battery.

Though some voltage is required to make the alternator operate, aside from that, the alternator needs to be in good condition to work. Therefore, putting a new battery in the car won't make a bad alternator operate. Check the wiring going to the alternator and if it is in good condition and the drive belt is tight, have the alternator checked...many larger parts stores will do that for you free.

This could be caused by a faulty voltage regulator, but since it has happened on more that one alternator, that can't be the problem, right? The next thing that I would look at would be a defective or loose belt. Also check the tensioner to make sure it is working properly and is keeping tension on the belt. If the belt is slipping or is worn out, it will cause voltage fluctuations. You may want to look at changing or at least inspecting the belt. Hope this helps and best wishes.

I've put in hundreds of alternators sometime a new one doesn't work properly you heed to check the voltage output of the vehicle running to see if it's charging or simple remove the negative battery cable while the vehicle is runnig, if it keeps running the alternator is working if it's dies it's not but you need to know the voltage output most vehicles it's 13.5 min.